This invention relates to a data recording method and a data recording apparatus for recording data transmitted from, e.g., a computer on an azimuth track on a magnetic tape by a rotary head.
In a computer, it has been a practice to transfer data written on, e.g., a hard disc to a data recorder known as data streamer, e.g., once a day for recording the data thereon for protection.
As such data recorder, a commonplace analog audio tape recorder has frequently been employed. Nevertheless, with such analog audio tape recorder, not only is the consumption of the magnetic tape increased, but also data recording and transfer takes a significant time because of the low data transfer rate during recording. In addition, since high speed search is not possible with the analog audio tape recorder, the so-called locating, that is, searching for the leading end portion of desired data, is also time-consuming.
Thus it has been a practice to employ a helical scan digital audio tape recorder, or so-called DAT, employing a rotary head, as the data recorder.
When the DAT is employed as the data recorder, data from a host computer is converted into DAT format data before being recorded. With the DAT format, two azimuth tracks T.sub.A, T.sub.B, produced with one complete revolution of two heads having different azimuth angles, make up a frame, and 16-bit PCM audio data are recorded by employing the interleaving technique, with the frame as a unit, as shown in FIG. 1. Each track is constituted by 196 blocks, each block being made up of 36 bytes. Both 34 end blocks make up a sub-area and central 128 blocks make up a main area.
Looking from a track end, each sub-area is divided into a margin domain, a sub-code PLL preamble domain, a first sub-code domain, a post-amble domain, adjacent block-to-block gap domain, automatic track finding (ATF) signal domain, adjacent block-to-block gap domain, data PLL preamble domain, adjacent block-to-block gap domain, ATF signal domain, adjacent block-to-block gap domain, sub-code PLL preamble domain, second sub-code domain, post-amble domain, adjacent block-to-block gap domain and a margin domain. The first and second sub-code domains are each constituted by eight blocks, while the remaining domains are constituted by respective predetermined numbers of blocks.
The main area is made up of 128 data blocks. Each data block is made up of a synchronization signal, a PCM-ID, a block address, and a parity, each of a one byte, and 32-byte main data domain, as shown in FIG. 2.
If the main data are audio signals, the main data are 16-bit L-channel PCM audio data and 16-bit R-channel PCM audio data. The 16-bit PCM audio data is arrayed in the main area of a frame, that is, two tracks, along with the parity Q data, by employing the interleaving technique, as shown in FIG. 3. In this case, approximately 5760 bytes of data are recorded in the 1-frame main area.
Thus, with the DAT format, post-recording may be made, using the sub-area, by dividing each track into the main area and the sub-area.
The error correction code for the main data in the DAT format is the two-dimensional code, as shown in FIG. 4. The code has four code planes per track, each being coded in the C1 and C2 directions.
If the DAT is used as a data recorder, data transmitted from the host computer are 16-bit data and handled in the same manner as the PCM audio data. These data are formatted and recorded in the 1-frame main area. Two 16-bit data for the L and R channels are used, in which the upper four bits are format ID data and the lower eight bits are recorded as the logical frame number. The format ID indicates the format proper to the data recorder and the frame numbers of from 1 to 23 are appended for each unit of the logical frame number, such as 23 frames.
As the format of the data recorder employing the DAT, the European Computer Manufacturers Association (ECMA) provides DDS and DDS2 formats.
The DDS or DDS2 formats provide a device area from the physical beginning of tape (PBOT) and logical beginning of tape (LBOT) in the leading region consecutive to the leader tape as the areas for magnetic tape loading and unloading. The device area is followed by a reference area and a system area. The reference area is used as a physical reference when recording a system log in the system area. The system area is followed by the data area for recording data, which in turn is followed by an end-of-data (EOD) area.
The DDS2 format provides two partition tapes P1 and P2, each having the reference area, system area, data area and the EOD area. The system log (hysteresis information) for each of the partitions P1 and P2 is recorded in the system area of each of the partitions P1 and P2.
With the above DAT format, the C2 parity (Q) is arrayed at the center and even-numbered and odd-numbered samples are arrayed on both sides of the C2 (Q) parity, in order that, for error data interpolation, the odd-numbered and the even-numbered samples will be arrayed at the positions furthest from each other on the tape. However, this is not only meaningless with the DDS or DDS2 format which are not in need of interpolation, but also presents a problem that the portions of the tape-shaped recording medium corresponding to the start and end of sliding contact of the recording medium with the rotary head, that is, both terminal portions of the tape in the track direction, tend to be worn by repeated use, thus increasing the probability of data error generation in these portions.